Engine manufacturers have focused on improving engine design in order to minimise emissions of particulates and pollutants, and improve cleanliness and fuel economy. One of the improvements in engine design is the use of exhaust gas recirculation (EGR) engines. Heavy duty diesel vehicles may use exhaust gas recirculation (EGR) engines in efforts to reduce environmental emissions. Whilst improvements in engine design and operation have contributed to reducing emissions, some engine design advances are believed to have generated other challenges for the lubricant. For example, EGR is believed to have led to increased formation and/or accumulation of soot and sludge. Among the consequences of recirculating the exhaust gas through the engine are different soot structures and increased viscosity of the oil at lower soot levels, compared with engines without EGR.
Increased soot-mediated oil thickening is common in heavy duty diesel engines. Some diesel engines employ EGR. The soot formed in an EGR engine has different structures and causes increased viscosity of engine lubricant at lower soot levels than formation of soot in the engine without an EGR.
Viscosity improvers are often used to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature.
Dispersant viscosity modifiers (DVMs) made from ethylene-propylene copolymers that have been radically grafted with maleic anhydride and reacted with various amines have shown desirable performance to prevent oil thickening in diesel engines. Aromatic amines are said to show good performance in this regard. DVMs of this type are disclosed in, for instance, U.S. Pat. Nos. 4,863,623, 5,264,139, 5,264,140, 5,620,486, 6,107,257, 6,107,258, and 6,117,825.
U.S. Pat. No. 5,409,623 discloses functionalized graft copolymers as viscosity index improvers, comprising an ethylene alpha-monoolefin copolymer grafted with an ethylenically unsaturated carboxylic acid material and derivatized with an azo-containing aromatic amine compound.
U.S. Pat. Nos. 5,264,139 and 5,264,140 disclose polymers derivatized with a sulphonyl-containing aromatic amine and an amide-containing aromatic amine material respectively.
Other dispersant viscosity modifiers have been contemplated in a variety of applications including U.S. patent applications Ser. No. 11/568,051, and 61/118,012; and International Application WO publication WO 2010/014655 A1.
U.S. patent application Ser. No. 11/568,051 discloses soot dispersants derived from esterified maleic anhydride-styrene interpolymers functionalized with nitrogen-containing moieties.
International Application WO publication WO2010014655 A1 discloses alpha olefin maleic anhydride (AOMA) interpolymers which may be esterified and further functionalized with amines having at least one condensable N—H group.
U.S. application 61/118,012 (also relating to International Patent Application WO2010/062842) discloses olefin polymers functionalized by grafting with an unsaturated carboxylic acid material and derivatized with aromatic amines having three or more non-contiguous aromatic groups.
Other publications disclose the possibility of dispersants with aromatic groups.
U.S. Pat. No. 5,182,041 discloses polyolefin based dispersants functionalized with an ethylenically unsaturated acylating agent and reacted with an amino-aromatic polyamine to produce antioxidant dispersants.
U.S. Pat. No. 6,051,537 discloses hydrocarbyl dispersants made from polyolefins functionalized with monounsaturated mono acid materials selected from acrylic acid, methacrylic acid and cinnamic acid reacted with amines, alcohols and/or aminoalcohols. These polyolefins have number average molecular weight in the range 1500 to 5000.